The present invention relates generally to a lighting assembly with load detection capability for reliably driving semiconductor light-emitting elements. More particularly, the present invention relates to a lighting device for performing DC lighting control of a semiconductor light-emitting element such as a light-emitting diode (LED) or the like, based on detection of the presence or absence of said light-emitting element.
In various conventional lighting devices that function to supply a DC current from an input DC power source to a semiconductor light-emitting element through a switching power converter, at power-on a DC starting current is fed to a control circuit associated with the converter to initiate a switching operation. A feedback current from the converter is subsequently supplied to the control circuit. Thereby, the converter is controlled so that the switching operation is started when the semiconductor light-emitting element is connected and the switching operation is not started when the semiconductor light-emitting element is not connected.
A switching power converter in various known examples includes a smoothing capacitor at an output terminal. To stabilize optical output, it is preferred that the capacitance of the smoothing capacitor is relatively large. However, upon turning the light off or during dimming control, while an electric charge remains in the smoothing capacitor the optical output of the semiconductor light-emitting element may not lower accordingly, possibly making a poor impression on the user regarding the control response. Thus, it can be considered as desirable to connect a discharge resistor in parallel to the smoothing capacitor.
However, when the discharge resistor is connected in parallel to the smoothing capacitor, even if the semiconductor light-emitting element is not connected, a switching operation may be initiated by a DC current supplied through the discharge resistor.
When the smoothing capacitor provided at the output terminal of the switching power converter has a relatively large capacitance, the switching power converter may be started by a charging current flowing through the smoothing capacitor at power-on. In this case, a problem occurs that even if the semiconductor light-emitting element is not connected to the circuit, the switching operation is maintained by a feedback current from the switching power converter. Further problems may occur in that even where the semiconductor light-emitting element is disconnected from the circuit after start of the switching operation, the switching operation may be maintained by the feedback current from the switching power converter.